Spherulitic Layer Research Articles

New insight on spatial localization and microstructures of calcite-aragonite interfaces in adult shell of Haliotis tuberculata: Investigations of wild and farmed abalones by FTIR and Raman mapping

In the present study, we investigated the shell microstructures of the gastropod European abalone Haliotis tuberculata in order to clarify the complex spatial distribution of the different mineral phases. Our studies were carried out with a standardized methodology on thirty adult European abalone H. tuberculata (5–6 cm long) composed of 15 wild individuals and 15 individuals taken from the France Haliotis hatchery. The macroscopic (binocular) and microscopic observations coupled with Fourier Transform Infrared Spectroscopy (FTIR) and Raman vibrational analysis allowed to unambiguously detect, identify and localize calcite and aragonite. For the first time it has been shown that calcite is present in 100% of farmed and wild adult shell. The microstructural details of the calcite-aragonite interfaces were revealed by using both confocal micro-Raman mapping and Scanning Electron Microscopy (SEM) observations. Calcite zones are systematically found in the spherulitic layer without direct contact with the nacreous layer. The calcite area - nacreous layer interface is made of a thin spherulitic layer with variable thickness from a few micrometers to several millimeters.In order to contribute to a better understanding of the biomineralization process, a model explaining the hierarchical arrangement of the different phases of calcium carbonate is presented and discussed. Finally, it has been shown that these calcitic zones can be connected to each other within the shells and that their spatial distributions correspond to streaks perpendicular to the direction of length growth.

Biomineralization in Polychaete Annelids: A Review

Polychaete annelids are a very important group of calcifiers in the modern oceans. They can produce calcite, aragonite, and amorphous phosphates. Serpulids possess very diverse tube ultra-structures, several unique to them. Serpulid tubes are composed of aragonite or calcite or a mixture of both polymorphs. The serpulid tubes with complex oriented microstructures, such as lamello fibrillar, are exclusively calcitic, whereas tubes with prismatic structures can be composed either of calcite or aragonite. In serpulids, the calcareous opercula also have complex microstructures. Evolutionarily, calcitic serpulid taxa belong to one clade and the aragonitic taxa belong to another clade. Modern ocean acidification affects serpulid biomineralization. Serpulids are capable of biomineralization in extreme environments, such as the deepest part (hadal zone) of the ocean. The tubes of calcareous sabellids are aragonitic and have two layers, the inner irregular spherulitic prismatic layer and the outer spherulitic layer. The tube wall of cirratulids is composed of aragonitic lamellae with a spherulitic prismatic structure. In some other polychaetes, biominerals are formed in different parts of the animal body, such as chaetae or body shields, or occur within the body as granule-shaped or rod-shaped inclusions.

(Invited) Modeling Morphology Distribution in Injection Molded Polypropylene Parts

The UNISA code, a software for the simulation of injection molding developed at the University of Salerno, considers a series of specific models to consider several aspects of the mutual effect of flow and crystallinity: the effects of temperature, pressure and flow on relaxation times, the effect of crystallinity on viscosity, the effect of flow on nucleation density and spherulitic growth rate. Each of the effects mentioned above was experimentally analyzed and described by a model for the iPP grade considered in this work. The combination of all these specific models becomes a model for the morphology evolution during polymer processing. In order to verify the accuracy of the predictions, a series of injection molding tests were obtained applying a system which allows to control the cavity surface temperatures. This technique allows to keep, for assigned time intervals, the cavity surface temperature at intermediate values between injection and cooling channels temperatures. A modulation of the level of the cavity surface temperature and of the time, it was kept active, allowed to control the final sample morphology all the way from the complexity of a standard injection molded part down to a completely (skin and shear layers free) spherulitic structure. The fibrillar layer morphology was related to the achievement of critical values of both the molecular stretch and the mechanical work, the latter being performed after the achievement of the critical molecular stretch. The dependence of the morphological layers (skin, shear, spherulitic layers, the latter including the transition from the shear zone) thicknesses upon the heating conditions was satisfactorily described by the models adopted.

The new order Mixosiphonata (Cephalopoda: Nautiloidea) and related taxa; estimations of habitat depth based on shell structure

The new order Mixosiphonata is characterized by its siphuncular structure. The order contains the ectocochleate cephalopods Boggyoceras centrale n.gen. et n.sp. (Carboniferous) and Zhuravlevia insperata (Cretaceous); both are orthocones. The bactritoid-like coleoid Ctenobactrites lesliensis (Carboniferous) has a similar siphuncular structure and is therefore, provisionally included in this new order. In the new order Mixosiphonata, the proximal part of the septal neck has the same structure as the septum from which it originates, whereas the entire distal part is composed of prismatic and spherulitic layers embedded into a chitinous substance. Also the connecting ring consists of prisms and spherulites embedded into chitinous substance, but the calcareous elements are smaller than those in the distal part of the septal neck. The structure of the connecting ring and septal neck differs from the 13 types of siphuncular structures in nautiloids, ammonoids and coleoids that are currently known. The siphuncular structure in the Ordovician cephalopod Bactroceras avus is described and compared with that in the mixosiphonates. The shell strength indexes derived from the extant Nautilus cannot be used for estimations of habitat depth in most, if not all, known externally shelled cephalopods because in the fossil cephalopods the siphuncular structures are different from that of extant Nautilus, and therefore, the mechanical strength of the siphuncles in the fossil shells and Nautilus shell is not comparable.http://zoobank.org/urn:lsid:zoobank.org:pub:6FE8CDBD-E99D-4055-93BA-22618E75CD52http://zoobank.org/urn:lsid:zoobank.org:act:56582CE7-7750-4937-98C0-5113CB0E896Ehttp://zoobank.org/urn:lsid:zoobank.org:act:7B9AF88B-4243-4418-957C-57EAF2CF2EDAhttp://zoobank.org/urn:lsid:zoobank.org:act:EB8874EB-C20F-41D7-8B70-6814378AFF13

Crystal growth-induced reconfiguration of the biopolymer framework in shell biomineralization

In the field of shell biomineralization, one of the major challenges is to understand the interplay between the biopolymer framework and crystal growth. The widely accepted model proposes that the framework is pre-formed and stable, which directs the subsequent crystal growth. However, it remains unanswered whether the crystal growth can inversely influence the framework's configuration. Here, we find that, in the silver-colored spherulitic layer of a bivalve shell, the framework is reconfigured during mineralization. This result may provide a new direction in the study of shell biomineralization.

Slumping and a sandbar deposit at the Cretaceous-Tertiary boundary in the El Tecolote section (northeastern Mexico): An impact-induced sediment gravity flow

Slumps affecting uppermost Mendez Formation marls, as well as the spherulitic layer and basal part of the sandy deposits of the Cretaceous-Tertiary (K-T) boundary clastic unit, are described at the new K-T El Tecolote section (northeastern Mexico). These K-T clastic deposits represent sedimentation at middle-bathyal water depths in channel and nonchannel or levee areas of reworked materials coming from environments ranging from outer shelf to shallower slope via a unidirectional, high- to low-density turbidite flow. We emphasize the development and accretion of a lateral bar in a channel area from a surging low-density turbidity current and under a high-flow regime. The slumps discovered on land and the sedimentary processes of the K-T clastic unit reflect destabilization and collapse of the continental margin, support the mechanism of gravity flows in the deep sea, and represent important and extensive evidence for the impact effects in the Gulf of Mexico triggered by the Chicxulub event.

Synchroneity of the K-T oceanic mass extinction and meteorite impact: Blake Nose, western North Atlantic

A 10-cm-thick layer of green spherules occurs precisely at the biostratigraphic boundary between the Cretaceous and Paleogene (K-T boundary) at Ocean Drilling Program Site 1049 (lat 30°08′N, long 76°06′W). The spherulitic layer contains abundant rock fragments (chalk, limestone, dolomite, chert, mica books, and schist) as well as shocked quartz, abundant large Cretaceous planktic foraminifera, and rounded clasts of clay as long as 4 mm interpreted as altered tektite glass probably derived from the Chicxulub impact structure. Most of the Cretaceous foraminifera present above the spherule layer are not survivors since small specimens are conspicuously rare compared to large individuals. Instead, the Cretaceous taxa in Paleocene sediments are thought to be reworked. The first Paleocene planktic foraminifera and calcareous nannofossil species are recorded immediately above the spherule bed, the upper part of which contains an iridium anomaly. Hence, deposition of the impact ejecta exactly coincided with the biostratigraphic K-T boundary and demonstrates that the impact event was synchronous with the evolutionary turnover in the oceans. These results are consistent with a reanalysis of the biostratigraphy of the K-T boundary stratotype, which argues that shallow-marine K-T boundary sections are not biostratigraphically more complete than deep-sea K-T boundary sites.

Skeletal Ultrastructure in Some Articulate Cyclostome Bryozoans

AbstractThe ultrastructure of the calcareous skeleton is described in 11 species of articulate cyclostome bryozoans with elastic joints. Ten species have interior walls comprising semi‐nacreous and pseudofoliated fabrics without a precursory granular layer. Exterior walls consist of outer, finely granular and planar spherulitic layers, succeeded by semi‐nacreous and pseudofoliated fabrics like those of interior walls. Outer fabrics are calcified as longitudinal strips, each corresponding to a planar sphcrulitic unit. Articulation surfaces comprise ring diaphragms of very fine granular fabric with concentric laminations. The semi‐nacre of walls adjacent to ring diaphragms contains minute holes. Crisulipora occidentalis is unique in having interior walls of transverse fibres succeeded by pseudofoliated fabric, articulation surfaces festooned with deep pits but lacking well‐differentiated ring diaphragms, and pseudopores containing sieve‐like closure plates. The ultrastructure of most articulates resembles tubuliporine cyclostomes with dominantly semi‐nacreous walls, although the lack of precursory granular fabric in the interior walls and the presence of subcircular tablets of semi‐nacre (without six‐fold sectoring) may be peculiar to articulates. In contrast, Crisulipora is more similar to other tubuliporines with transverse fibres. evidence which, together with other skeletal characters, suggests that Crisulipora evolved jointing independently of the rest of the articulate cyclostomes.

Skeletal Ultrastructures in some Cerioporine Cyclostome Bryozoans

Abstract The ultrastructure of the calcareous skeleton is described in nine species of Recent cyclostome bryozoans belonging to the suborder Cerioporina. Two species of Heteropora have interior zooecial walls comprising a granular precursory layer followed by a thick layer of transverse fibres and a subordinate foliated fabric with, in mature proximal walls, a semi‐nacreous layer. The remaining seven species have interior walls with no transverse fibres and instead predominantly comprise a distally‐imbricated, regularly foliated fabric overlying a granular precursory layer. Older, proximal surfaces often have abundant screw dislocations, but true semi‐nacre is absent. Basal walls comprise an outer finely granular precursory fabric and planar spherulitic layer, succeeded by the same ultrastructural succession seen in the interior zooecial walls of the respective groups. Exterior walled diaphragms, peristomes and gonozooids similarly comprise an external fabric of planar spherulitic calcite, lined internally by the predominant fabric seen in the interior walls. Ultrastructurally, therefore, cerioporines may be split into two groups with different fabric suites, the first resembling cinctiporids and many tubuliporines in having interior walls with fabrics of transverse fibres, foliated crystallites and semi‐nacre; and the second resembling the rectangulates Lichenopora and Disporella in having interior walls comprising only the foliated fabric. These findings support the close phylogenetic relationship between cerioporines and other cyclostomes but suggest that the cerioporines may constitute either a diphyletic or a paraphyletic group.

Travertine-cemented screes on the serpentinite seacliffs of Unst and Fetlar, Shetland

AbstractScrees on high serpentinite sea cliffs in Shetland have been internally cemented by deposits of brucite, hydromagnesite and aragonite since the last glaciation. These minerals have been deposited from solutions originating as rain (often contaminated with salt spray), which fell on the serpentinite screes and dissolved Mg and minor amounts of Ca from the more finely divided and powdery scree components. As the solutions filtered down through the screes they deposited cements in the form of spherulitic layers of brucite and hydromagnesite with minor amounts of aragonite. At sea level the Mg-rich solutions mingled with sea water impregnating the scree and there cementation within the scree took place by the crystallization of plush-type layers of aragonite on the serpentinite fragments.

Crystalline domains as trapping states in amorphous materials

The photoconductivity and thermostimulated currents were measured on amorphous and spherulitic layers of oligo(ethyleneoxy) 2,5-di(anilino)terephthalate. The crystalline domains in the amorphous phase form new traps, c. 0,6 eV deep.

Structure and morphology of thermally oxidized high density polyethylene pipes

AbstractThe effects of thermal oxidation on the‐ molecular structure and on the morphology of a series of high‐density polyethylene pipes have been studied “as received” or after service. The existence of a 40 to 170 μm thick oxidation skin was established, the structure and morphology of which were characterized by gloss measurements, scanning electron microscopy, polarized microscopy, infrared spectroscopy, gel measurements, and differential scanning calorimetry. The skin surface frequent contained craterlike structures, 25‐50 μm in diameter, whereas small‐scale structures occurred much less frequently than in non‐oxidized surfaces, and the gloss increased significantly. The presence of a carbonyl concentration gradient through the skin was established, and the gel measurements also indicated a crosslink gradient. The skin was found to be composed of a top layer with a mainly non‐spherulitic structure of very low crystallinity and melting point and a large‐scale spherulitic layer with a crystallinity and melting point slightly below the corresponding bulk values. The formation of this brittle surface layer and its effect on the long‐term fracture performance of the pipe are discussed.

A study of traps for current carriers in organic solids The effect of crystallinity on ethyl 2,5-di(anilino)-terephthalate and its oligomer

The dark electric conductivity, photoconductivity, thermostimulated currents (TSC) and space-charge-limited currents (SCLC) were measured on amorphous, polycrystalline and spherulitic layers of ethyl 2,5-di(anilino)terephthalate and of its oligomer. The electric behaviour is considerably influenced by processes of trapping of charge carriers. The activation energy of photoconductivity is determined by the trap depth. The crystalline and spherulitic domains in the amorphous phase form new traps, ca. 0·6 eV deep.